Building the Meat Sphere

[aion]

A recent thread brought up new Meatball clone, Aion's Spectron. The build doc has many interesting observations, which I thought I'd present here as of interest to all Meatball fans.

The Spectron wouldn't have been half as good if it wasn't for all the information in this thread... which, hard to believe, just turned a decade old on Tuesday. Thanks to everyone who's contributed along the way - including sharing your failures and frustration, since that's where most of the improvements come from.

[Zoot]

Hey idy,
Thanks for the new Meat Sphere tips. Aion is right about the LDRs. I just tried the GL5537-1s.
Tone seems in general brighter, and the effect is more scooped. Just some of the perfect sounds you want to hear from a great envelope like this one.
I had some noisy clipping with color at max with the VTL5C3s. It completely disappears with those LDRs, and with color at max and other more "radical" settings, the pedal whistles. I tried 5mm and 10mm green diffused LEDs uncovered, and 5mm ones covered (picture).
I thought that with the 10mm the sound was too bright, and the envelope too "whistly". No much difference between covered and uncovered ones. I opt for uncovered, just because they look cooler. The vactrols were retired.
Thanks again.
Zoot

[idy]

I'm interested in this "whistle" business. Is this a high pitched whistle when the filter is on full?

Since that sounds like feedback it would make sense that you get it when the "color" (really feedback) knob is up high.

Are you saying that with 5mm LEDs the whistle is gone?

[Zoot]

I'm interested in this "whistle" business. Is this a high pitched whistle when the filter is on full?

Since that sounds like feedback it would make sense that you get it when the "color" (really feedback) knob is up high.

Are you saying that with 5mm LEDs the whistle is gone?

The whistle doesn't sound abnormal, just the effect at its max indeed. I'm going to sleep now (GMT+1), but can soon post a sound sample. My impression is that the whistle is more frequent (not only at max) with the big LED indeed, but I can make it with the 5mm as well.
Cheers

[idy]

I haven't yet tried the GL5537-1, but I have some now. They actually test the same as the assorted ones I already had, which is to say that in ambient room light the light resistance is pretty low, under 2k. I should probably have a test with LEDs at levels of light like in circuit.

The last Meatsphere I made I used the old ones and ended up happier with a series resistor, I think less than 10k, because that seemed around the target value. It sounded less harsh, didn't 'flip out' didn't 'go too far' for my taste.

[kato]

Don't be this guy who lifted two pads from a perfectly working Meatsphere because he read roll-your-own vactrols are better than the VTL5C3's.



Or don't be so lazy that you can't unbox the thing and remove them properly from the bottom.

I hate to do it, but I'm gonna clip the leads and waste these two vactrols so I don't lift any more pads! These two pads appear to be not-connected to any traces on the reverse side so the fix should be pretty easy.

PS, hi guys, thanks for all the helpful tips in this thread.

[kato]

I probably should've left well enough alone because it was working great with the VTL5C3's.

I'm thinking my LEDs are too bright. I've tried two different pairs now. I get filter, but no envelope. It no longer quacks, just whistles and whines. Rapidly turning the Intensity knob mimics a wah pedal, but it no longer auto-wahs.

Does the roll-your-own vactrol need to be in the dark for the envelope to quack? I figured closing the lid would make it dark enough. But maybe the light from each neighboring vactrol is affecting the LDRs.

If anyone has any tips, I'd love to hear them.  Thanks.

[idy]

The back on should be dark enough.

It is possible to "pad" the LDR with additional resistors to make it not so harsh. The value of LDR makes a big difference. I still have not used the suggested GL-55371.

[PRR]

When I was prototyping a recording limiter, I had to work in the dark (windowless concrete block room) AND with a heavy cardboard shield over each opto-resistor. Light leaked under the edge of the shield. I had a highly-masked desk-lamp to read my meters at the verge of visibility.

So without seeing just what you are doing, I would advise you DARKER DARKER DARKER until you can show what minimum level messes your system. Your effect may not be as fussy as my limiter, because the "normal" mode of the recording limiter is NO-light (full signal) while your FX may be more/less light.

[kato]

The back on should be dark enough.

It is possible to "pad" the LDR with additional resistors to make it not so harsh. The value of LDR makes a big difference. I still have not used the suggested GL-55371.

Thanks. It never occurred to me that maybe the LDR is actually the problem!
I've tried orange 5mm LEDs which may have been too bright at 2500mcd. (I've read orange-yellow-and-green should all be within the spectrum picked up by the LDR.) They were "always on" to some degree even with no signal, but brighter when the guitar strummed. I also tried green LEDs in 5mm and 3mm with the same problem.

This batch of LDRs I bought were possibly a little too cheap and may be out of spec cast offs. Maybe I should buy a known pair of LDRs. Do you remember which model you're using?



And yeah, I bumped the 100Ω resistors to 300Ω per the Aion documents, but perhaps I need to try even higher resistance into the LEDs.

[kato]

When I was prototyping a recording limiter, I had to work in the dark AND (windowless concrete block room) with a heavy cardboard shield over each opto-resistor. Light leaked under the edge of the shield. I had a highly-masked desk-lamp to read my meters at the verge of visibility.

So without seeing just what you are doing, I would advise you DARKER DARKER DARKER until you can show what minimum level messes your system. Your effect may not be as fussy as my limiter, because the "normal" mode of the recording limiter is NO-light (full signal) while your FX may be more/less light.

Thanks PRR. I'll try DARKER by wrapping them in electrical tape before I swap out the LEDs yet again. The pads are now lifted from all the LED swapping.  I've noticed a slight wah effect is created when I move the box around with the back door open, even from a rather distant overhead light.

BTW, thanks for all your advice over the years. I often think of advice you gave me decades ago when I was first starting out. For example, last night: "that probably wasn't enough heat to burn out a silicon diode" based on something PRR once said. For real. A lot of your comments have stuck with me over these years. I appreciate it.

[PRR]

Red LEDs work perfectly fine. People who think PhotoRs are color-fussy have not tried it. "Red is best" because historically cheapest (less true now that all are cheap), good sensitivity, and low forward voltage.

[idy]

Aion recently did the deep dive for their Spectron, and suggest GL-55371 ldr as faithful in performance to original MeatBall. Yes the LDRs matter.

The originals used green LEDs but I trust PRR that color is not important, although it will light with less voltage so that may change the sweep. Socket and experiment if you can! That's how I came to add series resistors to the (unknown model) LDRs in my last build. I think they are not supposed to go below 10k with the LEDs on....

The original meatball also did not use a light shield, although their rolled metal enclosure has unknown light shielding properties.

[Govmnt_Lacky]

As per the originals (as said by Dan Coggins) the Meatball ,Doppelganger, and Ring Stinger all use 20-30K On/2M Off LDRs and Diffused Green LEDs. The Flanger and Wobulator used 20-30K On/20M Off LDRs and used a mix of Green Diffused and Low-Brightness water clear Green LEDs. Although I have always used Diffused Green throughout in all builds successfully.

My suggestion is to look at the datasheets for the LDRs. This will tell you the nominal spectrum that the LDRs react to. Most on the market fall squarely within the Green color range.

Good Luck 

[orangetones]

Hello all... Would increasing the feedback resistor on the envelope follower be a reasonable way to increase the sensitivity of this circuit?

[tuckster]

My Spectron pops very loud when using the Range selector. Is there a way to avoid that?
Would a pull-down on pin B & C of the rotary switch help?

[idy]

Disclaimer: I have built meat spheres, but that is the same circuit.
When I tested them today they popped the fruit time, but not again even an hour alter, but I don't change the range setting when performing.

If the popping is because of charged caps, you would tend to notice it louder on  the lower frequency settings than higher (bigger vs smaller caps.)
You should be able to experiment with pulldown resistors, but not on the center lugs of the switch, on the peripheral lugs, C2 C3 C4 and B2 B3 B4 on the schematic. So the "hanging" caps can discharge when not in use.

[Ben N]

Without reading through all 36 pages... Since Taylor is closing up shop, I'm thinking about ordering a pcb. Can anyone tell me if any of the parts have gone unobtanium over the years? (I know about the vactrols and the roll-your-own subs.)

[Taylor]

I think the only special thing besides the optos would be the LM1458, and I'm seeing plenty of those on Mouser right now.

[Ben N]

Thanks, Taylor, order already placed.